Application of item response theory modelling to measure an aggregate food security access score

Food security measurement is of paramount importance as it guides governance, policy formulation and intervention projects targeting and monitoring and evaluation. The measurement of food insecurity has proven to be a difficult task owing to the multi-dimensionality of the construct and different measurements have been developed to measure different dimensions of food insecurity. However, it is difficult to apply the different measurements to a holistic food security measurement as their classification might not agree. The current study proposes a composite food insecurity indicator by aggregating items from Household Dietary Diversity Score (HDDS), Household Food Insecurity Access Scale (HFIAS) and Months of Inadequate Household Food Provision (MIHFP) for Windhoek households' data into a single measure using the Rasch Testlet Response Model. The composite measure was internally validated against the HDDS, HFIAS and MIHFP and externally validated against household income and the Lived Poverty Index (LPI) using Spearman's Rank Correlation and Cohen's Kappa. The validation results suggest that the metric could be a promising measure of aggregate food insecurity worth further investigation and discussion. However, more research is needed in coming up with cut-points for categorizing households into food insecurity statuses. In addition, the metric has only been computed and tested on a single urban sample in the Global South and hence it is not generalizable to different setups. Other researchers who might want to use the index can try to estimate and validate the index in different scenarios and suggest ways the index can be improved.